How Buildings Provide Shielding from a Nuclear Explosion

Figure 1: Building as shielding: Numbers inside buildings are percent reduction of exposure inside compared to exposure outside. Figure 2: Building as shielding: Numbers represent a "dose reduction factor," not a percentage. A dose reduction factor of 200 indicates that a person in that area would receive 1/200th of the dose of a person out in the open. White graphics inside the 50, 80, 100, and 200 boxes simulate persons gathered together. The number 2 and 3 outside the building also represent a "dose reduction factor" outside the building related to shielding by the building itself, compared to exposure in open areas outside in a direct line with the radiation event center. Source: Armed Forces Radiobiology Research Institute's Medical Effects of Ionizing Radiation Course on CD-ROM (1999) Buildings provide considerable protection from fallout A brick building provides better protection than does a brick veneer building, which provides better protection than a frame building. Multiple stories increase protection as well. The interior of a one-story building reduces exposure by 50 percent. A level below ground reduces exposure by 90 percent. Additional levels provide more shielding and increase the overall effectiveness above and below ground. In the five-story building illustration (see Figure 1), the middle floors provide better shielding than the ground and topmost floors because fallout that covers the ground emits gamma radiation along with fallout that covers the exterior surfaces of the building. Moving to a higher floor in the building increases the distance from the ground source but, at some point, increases exposure from the source on the rooftop. The best option is to move to the center of the building away from the exterior walls and below ground, if possible, or to a middle floor above ground. Note how the position in the building and surroundings affect the percentage by which exposure is reduced.